Differential froth flotation of molybdenite and copper sulfides utilizing &#34;nokes&#34; reagent



United States Patent DIFFERENTIAL FROTH FLOTATION 0F MOLYB- DENITE AND COPPER SULFIDES UTILIZING NOKES REAGENT Burton Corbett and James J. Bean, Miami, Ariz., assignors to Miami Copper Company, Division of Tennessee Corporation, New York, N.Y., a corporation of Delaware No Drawing. Filed Apr. 14, 1965, Ser. No. 447,962

8 Claims. (Cl. 209-167) ABSTRACT OF THE DISCLOSURE An improved process of differential froth flotation applied to a flotation pulp of molybdenite and copper sul' fides utilizing a Nokes reagent for depressing the cop per sulfides and a collector reagent for floating the molybdenite, wherein the flotation pulp is maintained at an unusually high pH, i.e. no lower than about 11.4 and preferably within a range of about 11.4 to 12.4.

The invention This invention relates to the separation by froth flotation of molybdenite from copper sulfides and other me tallic sulfides, such as iron sulfides, utilizing the so-called Nokes reagent as a depressant for the metallic sulfides other than molybdenite.

The Nokes reagent and process of employing same in the separation of molybdenite from other metallic sulfides, chiefly copper sulfides, by differential froth flotation are disclosed in detail by the Nokes et al. US. Patent No. 2,492,936. Such reagent and process have been and are being extensively employed in the milling of copper sul-.

fide ores and concentrates which contain molybdenite. Because of the ease of production and the low cost, the most popular form of the Nokes reagent are disclosed by that patent is a sodium thiophosphate produced by reacting sodium hydroxide and phosphorous pentasulfide.

Although the Nokes reagent can be employed by adding it to a copper sulfide flotation concentrate containing molybdenite, without prior conditioning of such concentrate, it is ordinarily preferred to condition the concentrate by treatment with acid and alkali, all as set forth in the aforesaid Nokes patent, for removing froth collector coatings from the minerals prior to flotation with the Nokes reagent. Even so, some trouble has been encountered with excessive frothing, and the process of Nokes US. Patent No. 2,811,255 was developedto overcome such trouble. This involves preliminary cleansing of the concentrate and repulping with fresh water following elimination of the liquid phase of the so-cleansed concentrate prior to flotation for the recovery of the molybdenite.

The present process utilizing the Nokes reagent not only overcomes, in large measure, the previously encountered trouble with excessive frothing, but gives cleaner separation of the molybdenite from the other sulfides and significantly improved recoveries, without resort to any preliminary cleansing of the concentrates.

The Nokes et a1. process, as disclosed in the patent and as practiced industrially, involves a pH for the flotation pulp of from about 9 to 10.5 and sometimes, but rarely, as high as 11. We have found, however, that a pH well above 11, usually not lower than 11.4 and often much higher, e.g. 12.4, provides highly useful results not heretofore achieved in the use of the Nokes reagent.

Accordingly, the principal feature of this invention is conditioned for one the use of the Nokes reagent With a flotation pulp raised in pH from the normal lower range to a significantly higher range.

The pH of the flotation pulp is raised in conventional manner by the addition of an alkaline reagent to the circult, preferably immediately prior to the molybdenite flotation step. The high pH float yields rougher concentrate containing a large part of the molybdenite. Such concentrate is easily upgraded by further flotation.

It is preferred to use either calcium or sodium hydroxide as the alkaline reagent, because of the ready availability and low cost of these materials. But a wide variety of other alkaline materials can be satisfactorily utilized.

Lime circuits are usual for copper flotation and, because lime is alkaline, regular mill water from such circuits can be advantageously utilized in the present process. This is an important factor in most mills, where water must be conserved. It is also important from the standpoint of eliminating need for filtration and repulping of the general copper sulfide flotation concentrates.

prior to flotation for the recovery of molybdenite.

As previously indicated, manageable froths result from making the molybdenite separation at high pH. It should be realized, however, that differences in type and grade of ore from place to place in the same ore body affect the operation and that there may be more froth at some times than at others.

It has been found that grinding in the final cleaning stages is often advantageous, and, also, that the use of sodium cyanide is sometimes helpful as an additional depressant for copper sulfides.

Numerous comparative tests have been run in the laboratory and in a pilot plant on samples of final copper concentrate taken at various times during usual mill operation from the pipe feeding the filters at the Copper Cities mill of the Miami Copper Company Division of Tennessee Corporation at Miami, Ariz. These have all demonstrated the utility and surprising character of the present process.

A typical test utilizing the invention was conducted as follows:

EXAMPLE I A sample of final copper concentrates, obtained as above and having a dry weight'of 955 grams, was diluted to 32% solids with mill water in a 600 gram laboratory Fagergren flotation machine. Two grams of lime (calcium hydroxide, U.S.P. powder) were added to the pulp and minute. The lime addition raised the pH of the pulp from its normal 10.4 to 11.95. Fifteen cubic centimeters of a dilute Nokes reagent (5.0 grams P 5 reacted with 6.5 grams of NaOH in cc. of water) was added to the pulp, together with three drops of stove oil. No frother was required. A flotation froth was pulled for five minutes. The following metallurgical results were shown by this test:

3 EXAMPLE II The following tabulation shows the results of three sets of comparative tests carried out in the laboratory in the same manner as the above, the first test of each set being without the pH adjustment of this invention:

1 Head calculated from assays and weights of Rougher Concentrates and [tougher Tail.

N Distribution, M08 percent Reagents, lbs/ton Set R0. Cone. R0. Tails N okes 02.0

Pilot plant operation has also demonstrated the effectiveness of the invention. Copper concentrate from the Copper Cities mill was taken as in the laboratory tests, but on a twenty-four hour basis. It was passed through a pilot plant having a capacity of one ton per hour and utilizing a flow scheme comprising rougher flotation using the Nokes reagent (sodium thiophosphate as before) as a copper depressant in a mill water circuit adjusted with lime to a high pH as compared with the normal, followed by five cleaning steps, regrinding of the fifth cleanerconcentrate, and three more cleaning steps to produce a final molybdenite concentrate.

The results tabulated below are from samplings over eight hour operating periods, and are representative of results that would be obtained in a commercial operation:

Other tests have shown that satisfactory molybdenitecopper separations can be made on metallurgical products very low in MoS content, irrespective of the copper mineralization, and that consistently good molybdenite recoveries can be obtained from all types and grades of sulfide copper concentrates. This is in contrast to results obtainable at the customary, relatively low pH of the flotation pulp.

'A series of tests was also made utilizing acid as in Example 7 of the Nokes et al. US. Patent No. 2,492,936 in comparison with no acid at both normal pH and the high pH of this invention. The Nokes reagent used in each instance was sodium thiophosphate. The results were as follows:

EXAMPLE IV Assay, Product Percent percent Distribu- Reagents,

Wt. MOSz tiou, percent lbs/ton Test No. 1 (pH 9.8)

100.00 0. 200 100. 0 Nokes (4.2). 1. 58 7.100 42. 8 H2804 (3.5). 98.42 0.150 57. 2 Lime (1.8).

Test No. 2 (pH 11.7)

100. 0 0.275 100.0 Nokes (3.35).

1. 81 12. 500 S2. 5 Lime (5.85). 98. 19 O. 050 17. 5 KD-38 (0.066)

Test No. 3 (pl-1 9.8)

Head 100.00 0.345 100.0 Nokes (5.8). R0. Conc. 4.82 6.800 94.8 KD-38 (0.076). R0. Tails"... 95. 18 0. 020 5. 2

Test No.4 (pH 11.7)

Head 100. 00 O. 344 100. 0 Nokes (5.6). R0. Cone"... 3. 97 8.200 94. 6 Lime (6.4). R0. Tails..." 90.03 0.020 5.4 KD-38 (0.073).

A comparison between use of the Nokes arsenic reagent, made in accordance with Example 20 of the Nokes et al. US. Patent No. 2,492,936, at normal pH and at high pH of the flotation pulp, showed results as follows:

EXAMPLE V Percent Assay, Distri- Pounds Product Wt. percent bution, Reagent per ton MoS percent Test No. 1 (pH 10.1)

0.279 100.0 N Arsenic"... 2. 19. 800 94.6 CaClz 5. 70 0.015 5.4 Lime 1. KD-3S 0.071

Test No. 2 (pH 11.5)

0.251 100.0 N Arsenic 2. 55 34. 900 90. 0 CaClz 5. 10 0. 025 10. 0 Lim 5. 70

For the purpose of showing the efiect of very high pH of the flotation pulp, a series of comparative tests were performed on grab samples taken from the same source of final copper concentrates as the foregoing examples. These tests and the results thereof were as follows:

CaO M502, percent Percent Dist.

Grams Lbs. lton Heads Tails Conct. Conct. Tails Nil Nil 10. 5 0. 279 0. 018 5. l 93. 7 6. 2.0 6.0 11.7 0. 235 0.020 8. 9 92. 0 8.0 6. 18. 12.0 0. 240 0.020 8. 1 92. 1 7. 9 24.0 72.0 12. 4 0.226 0. 020 12. 3 91. 0 9. 0

Whereas there are here described specific procedures presently regarded as the best mode of carrying out the invention, it should be understood that various changes can be made without departing from the inventive subject matter that is particularly pointed out and claimed herebelow.

We claim:

1. An improved process of differential froth flotation of a flotation concentrate of molybdenite and copper sulfides utilizing a Nokes reagent as a depressant for the copper sulfides, comprising subjecting a flotation pulp of mixed copper sulfides and molybdenite to at least a rougher stage of flotation in the presence of a collector for floating the molybdenite and of a Nokes reagent for depressing the copper sulfides, said pulp having a pH no lower than about 11.4.

2. A process according to claim 1, wherein the pH of the pulp is within the range of about 11.4 to 12.4.

3. A process according to claim 1, wherein the Nokes reagent is sodium thiophosphate.

4. A process according to claim 3, wherein the pH of the pulp is within the range of about 11.4 to 12.4.

5. A process according to claim 1, wherein the Nokes reagent is the reaction product of sodium hydroxide, sulfur, and arsenic trioxide.

6. A process according to claim 5, wherein the pH of the pulp is Within the range of about 11.4 to 12.4.

7. A process according to claim 1, wherein sodium cyanide is also present in the flotation pulp during the flotation operation as an aid in depressing the copper sulfides.

8. A process according to claim 7, wherein the pH of the pulp is within the range of about 11.4 to 12.4.

6 References Cited UNITED STATES PATENTS 12/1949 Nokes 209-467 10/1957 Nokes 209-167 10/1960 Henderson 209-167 11/1965 Moyer 209167 OTHER REFERENCES Froth Flot, 50th Anniversary Volume, Aimme, 1962, 10 pp. 386, 394, 395. TN 523 S 58.

HARRY B. THORNTON, Primary Examiner.

FRANK W. LUTTER, Examiner. 5 R. HALPER, Assistant Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No 3,375 ,924 April 2 1968 Burton Corbett et a1.

It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

Column 3, second table, fifth Column, th numerical values should be dropped down one Space to be in alignment with the second, fourth, and sixth lines, respectively, of the table, and cancel the bracket; third table, third column, line 1 thereof, "9.050" should read 0.050 Column 4, third table, first line thereof, in the heading, "M50 should read MoS Signed and sealed this 26th day of August 1969.

(SEAL) Attest:

Edward M. Fletcher, Jr. WILLIAM E. SCHUYLER, JR.

Attesting Officer Commissioner of Patents 

